netdev - Re: [PATCH] net: add missing skb_uarg refcount increment in pskb_carve_inside

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Message-ID: <e9b280b79ba444a68f5279cea77a84bf@huawei.com>
Date:   Fri, 14 Aug 2020 07:15:29 +0000
From:   linmiaohe <linmiaohe@...wei.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
CC:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Florian Westphal <fw@...len.de>,
        "martin.varghese@...ia.com" <martin.varghese@...ia.com>,
        "pshelar@....org" <pshelar@....org>,
        "dcaratti@...hat.com" <dcaratti@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        "Paolo Abeni" <pabeni@...hat.com>,
        Shmulik Ladkani <shmulik@...anetworks.com>,
        "Yadu Kishore" <kyk.segfault@...il.com>,
        "sowmini.varadhan@...cle.com" <sowmini.varadhan@...cle.com>,
        Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: add missing skb_uarg refcount increment in
 pskb_carve_inside_header()

Willem de Bruijn <willemdebruijn.kernel@...il.com> wrote:
>On Thu, Aug 13, 2020 at 2:16 PM Miaohe Lin <linmiaohe@...wei.com> wrote:
>>
>> If the skb is zcopied, we should increase the skb_uarg refcount before 
>> we involve skb_release_data(). See pskb_expand_head() as a reference.
>
>Did you manage to observe a bug through this datapath in practice?
>
>pskb_carve_inside_header is called
>  from pskb_carve
>    from pskb_extract
>      from rds_tcp_data_recv
>
>That receive path should not see any packets with zerocopy state associated.
>

This works fine yet as its caller is limited. But we should take care of the skb_uarg refcount for future use.
On the other hand, because this codepath should not see any packets with zerocopy state associated, then we
should not call skb_orphan_frags here.

Thanks.

>> Fixes: 6fa01ccd8830 ("skbuff: Add pskb_extract() helper function")
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>